Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

2. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

3. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

4. For obtaining high COP, the pressure range of compressor should be

Any value

High

Optimum

Low

5. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

6. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

7. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

8. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

9. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

Normal cooling

None of these

10. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

Page 2 of 4

11. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

12. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

10 tons

0.1 ton

13. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

14. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Carnot

Reversed Carnot

15. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

All of these

Room air conditioners

16. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

17. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

18. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Negative

Positive

19. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

20. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

8 bar

15 bar

Page 3 of 4

21. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

22. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Two heat exchangers

Three heat exchangers

23. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

24. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

25. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

26. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

27. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

28. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

15°C

10°C

29. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Low boiling point

Large latent heat

Good electrical conductor

30. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Page 4 of 4

31. Which of the following cycles uses air as the refrigerant?

Ericson

Carnot

Stirling

Bell Coleman

32. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

9: 1

1: 3

33. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Carbon dioxide

Freon

34. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.6

0.376

0.4

35. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

Capillary tubes

36. The boiling point of ammonia is

-77.7°C

-33.3°C

-30°C

-10.5°C

37. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

Involves no change in volume

38. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Centrifugal

Miniature sealed unit

39. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Always more than unity

Equal to unity

40. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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